TABLE 4.

Survival of IH11128 bacteria residing within Caco-2/TC7 cells as a function of days in culture postinfection^a

Day in culture	Viable intracellular bacteriab
6	3.23 × 104 ± 0.55 × 104 (100)
7	2.34 × 104 ± 0.35 × 104 (72)
9	1.77 × 104 ± 0.30 × 104 (55)*
11	1.20 × 104 ± 0.25 × 104 (37)*
13	1.14 × 104 ± 0.18 × 104 (35)*
15	1.24 × 104 ± 0.15 × 104 (38)*

^aThe cells at day 6 in culture were infected with IH11128 bacteria for 3 h at a concentration of 10⁸ CFU/ml. The infected cells were washed three times with PBS and then incubated with gentamicin (75 μg/ml) for 1 h. The infected cells were subsequently cultured in the presence of cell culture medium containing gentamicin (50 μg/ml), and the medium was changed daily to prevent extracellular replication of the remaining viable extracellular bacteria. The number of intracellular bacteria was determined as a function of the day postinfection at days 1, 3, 5, 6, and 9, corresponding to days 7, 9, 11, 13, and 15 in cell culture, respectively. 

^bResults are expressed as mean numbers of CFU/ml ± SEM. The values in parentheses are the percentages of remaining viable intracellular bacteria compared to bacteria that invaded the cells at day 6 in culture (100%). An asterisk represents a P value of <0.01 compared with intracellular bacteria at day 6 in culture.